The present invention relates generally to a hologram plate and its fabrication process, and more specifically to a hologram plate designed to replicate a hologram array comprising collective element holograms such as hologram color filters, and its fabrication process.
The present invention is also concerned with a multifaceted hologram plate and its fabrication process.
Further, the present invention is directed to the construction of a protective film for a hologram plate.
In JP-A 06-222361, etc., the applicant has already come up with a hologram-harnessing color filter for the purpose of greatly increasing the efficiency of utilization of liquid crystal display backlights, etc. This hologram color filter is basically made up of an array of a transmission type of collective element holograms capable of diffracting parallel light incident thereon at a specific wavelength and a specific angle of oblique incidence in such a way that it is converged on a specific focal distance position.
To use such a hologram array as a hologram plate to replicate another hologram array having similar properties by a hologram replication process, for instance, a first hologram plate is fabricated in the form of a computer-generated hologram (CGH). Then, the first hologram plate is replicated by the hologram replication process to fabricate a hologram plate, from which the final product is fabricated by a similar hologram replication process.
To replicate such a transmission type of collective element hologram array as mentioned above, the applicant has filed a patent application (JP-A 09-90860) to come up with a process wherein when replicas of the first plate and hologram plate are fabricated, the distance between the hologram plate and a hologram photosensitive material is fixed to substantially double the focal length of each element hologram to make a hologram replica having similar properties to those of the hologram plate. This process is now explained with reference to FIG. 12.
FIG. 12 is illustrative of how to fabricate a hologram array 5 providing a hologram color filter from a CGH array plate 7 in one single replication operation. A plate for a hologram array 5 providing a hologram color filter is constructed in the form of a CGH array 7. The distance from the relief surface of the CGH array plate 7 to a photosensitive layer 13 is fixed to 2f that is double the focal length f of each CGH 5″ so that a hologram photosensitive material 8 is spaced away from the CGH array plate 7. Laser light 9 having a specific wavelength is entered into the CGH array plate 7 at a specific angle of incidence, so that diffracted light 10, converged by the diffraction action of each CGH 5″ from convergent light to divergent light, and straightforwardly traveling transmitted light 11 interfere in the photosensitive layer 13 of the hologram photosensitive material 8.
Here let D represent the diameter of a recording area of each element hologram 5″ of the CGH array plate 7. Then, the diffracted light 10, once converged on a position P located at a distance f from the relief surface of each CGH 5″, is converged on a 2f position into a divergent light beam having the same diameter D. Accordingly, if the divergent light and the straitghtforwardly traveling transmitted light 11 interfere in the photosensitive layer 13 located at this position, the diameter of the hologram interference fringe recording area becomes equal to D, and the pitch between adjacent replicated element holograms becomes equal to that between adjacent element holograms 5″ of the CGH array plate 7 as well. In addition, when light traveling in the opposite direction to the transmitted light for hologram array replication is entered in the thus replicated hologram array from the glass substrate 12 side, the diffracted light is converged on a position P at a length f from the photosensitive layer 13 with hologram interference fringes recorded therein, and so has the same diameter as the focal length of each element hologram 5″ of the CGH array plate 7. In other words, a hologram array completely identical with the CGH array plate 7 is obtained.
The hologram array replicated from the CGH array plate 7 in such an arrangement as shown in FIG. 12 is then used as a hologram plate to obtain the end product. FIG. 13 is illustrative of one arrangement of how to carry out such second replication operation. In FIG. 13, H1 stands for an intermediate hologram array obtained by replication in the arrangement of FIG. 12. This intermediate hologram array H1 is again used as a hologram plate for replication purposes. In this case, the hologram photosensitive material 8 is located on the side of the plate 7 for the replication of the intermediate hologram array H1, and reconstructing illumination laser light 9′ is entered in the intermediate hologram array H1 from the opposite direction to the transmitted light 11 for the replication of the intermediate hologram array H1, and the distance from the diffraction surface of the intermediate hologram array H1 to the photosensitive layer 13 of the hologram photosensitive material 8 is fixed to 2f that is double the focal length f of each element hologram. When the reconstructing illumination laser light 9′ is entered in the intermediate hologram array H1 in such an arrangement, light 10′ diffracted by each element hologram of the intermediate hologram array H1 travels in the opposite direction to the diffracted light 10 of FIG. 12 and, once converged, is converted at the 2f position to a divergent light beam having the same diameter D. Accordingly, diffracted light 10′ and straightforwardly traveling transmitted light 11′ interfere in the photosensitive layer 13 located at this position as in the case of FIG. 12, so that an array of element holograms having the same focal length f is replicated and recorded at a pitch d in the area having the same diameter D.
The feature of this process is that a hologram similar in properties to the hologram plate can be fabricated even when the hologram plate is in no perfect contact with the replica. In what follows, the hologram replication process in such an arrangement will be called a double-focus replication process.
Incidentally, hologram photosensitive materials such as photopolymers are generally poor in marring resistance whether in an unrecorded state or in a state subjected to post-recording treatments. When replication is carried out with a hologram plate in close contact with a hologram photosensitive material, it is likely that the hologram on the hologram plate side is immediately damaged and some of the photosensitive material on the replication side peels off, depositing onto the hologram on the hologram plate side. Such depositions are hardly removable.
When a hologram has such a focal length as mentioned above, there is a variation in the focal length of replicas due to a contact gap at the time of replication, and a variation in gap thickness leads to a variation in the focal length of replicas.
It is desired that the zero-order light and first-order light diffracted by the hologram plate have substantially the same intensity at the position of the hologram photosensitive material. To this end, it is required to place the refractive index modulation under severe control. However, this control is difficult on practical levels.
The hologram (intermediate hologram array H1) used for the replication of the end products is herein called the hologram plate. When a hologram plate having only one hologram (hologram color filter) equivalent to one segment is used for the replication of such a color filter as mentioned above, however, replication efficiency becomes worse.
To avoid this, a process has been proposed in the art, which process makes use of a hologram plate obtained by translating a CGH plate 7 with respect to one large hologram photosensitive material 8 for a plurality of replication cycles wherein, for instance, four or eight holograms are exposed to light to form four or eight juxtaposed holograms in the hologram photosensitive material, so that four or eight holograms can be simultaneously replicated in one replication operation. Such a hologram plate with a plurality of juxtaposed holograms is called a multifaceted hologram plate.
As shown in FIG. 13, for instance, the multifaceted hologram plate is prepared in plural replication operations, using a CGH plate with respect to one; large hologram photosensitive material. However, when at least one of plural exposure operations (replication operations from the CGH plate) is improper, the resultant multifaceted hologram plate cannot be used or fails to provide a hologram plate having good replication efficiency.
In view of such prior art states as mentioned above, the first object of the present invention is to provide a hologram plate used with the double-focus replication process, which is integrated with a spacer to impart marring resistance thereto, and is integrated with a light absorbing layer to allow zero-order light and first-order light to have substantially the same intensity, and its fabrication process.
The second object of the present invention is to provide a multifaceted hologram plate which can have hologram segments of improved properties, can be used for efficient replication, and has improved durability, and its fabrication process.
The third object of the present invention is to provide an easily releasable protective film for a hologram plate, which prevents surface marring, wearing and contamination at the time of contact replication or removal of foreign matters.